1. Field of the Invention
The present invention relates to an automatic page detector. In particular, the present invention relates to an automatic page detector by using a sensor plate at each page of the book, an array of inductors just beneath the sensor plate and feedback loop of a LC oscillator to determine which page of a book is open.
2. Description of the Related Art
Automatic page detector is often used in an electronic reading book. Electronic book is a book containing a speech synthesizer which can play the contents of the book from a speaker. The “STORY READER” produced by Publication International Ltd, is a prior art of an electronic book with the function of an automatic page detector. This prior art uses a lot of magnets and reed switches as the sensors of the automatic page detector. When a magnet is in proximity of a reed switch, the two terminals of the reed switch will be closed. By detecting the state of each reed switch in an electronic book, we can determine which page of the book is opened. The disadvantage of this technology is the high cost of the reed switch. Besides, the thickness of the magnet is too thick and inconvenient to embed in the paper of an electronic book. The other prior art of an electronic book with automatic page detecting function is “Power Touch” produced by Mattel Canada Inc. In this product photo detection technology is used. A sensor consists of an infrared photo diode and transistor pair. A reflecting material is coated on some location of a page of the electronic book. The reflecting material can reflects the infrared light from the photo diode to the photo transistor. Input the status of each photo transistor to a microprocessor, which page of a book is open can be determined. Because of using photo diode and photo transistor, this technology is also not cost effective. Besides, the light from the environment can affect the photo transistor and make the wrong detection. One more prior art is the technology invented by the inventor (application Ser. No. 11/365,469). The technology uses a magnet and an inductor as sensor. Also, the thickness of the magnet is too thick and inconvenient to embed in the paper of an electronic book. Besides, when uses a magnet and an inductor as a sensor, the interaction between the magnet and inductor will causes magnetic hysteresis effect in the inductor. A close proximity of a magnet to an inductor will cause variation of the inductance of the inductor. The inductance of the inductor will not return to its original value even if the magnet leaves far apart from the inductor. And the frequency of the oscillator will depend not only on the distance between the magnet and the inductor but also on the history of the interaction between magnet and inductor, and makes it more difficult to determine the proximity of a magnet to an inductor.